Astronomers from Indian Institute of Astrophysics (IIA) have made a big find on how Blue Straggler Stars (BSS) form. These stars are hotter,brighter,and more massive than others in clusters. This work,with help from Italy,France,and United States, got published in Astrophysical Journal Letters.
BSSs have puzzled scientists for years because of their odd features and how they form. Theories suggested they gain mass from another star or merge with one. But hard proof was missing until now. India's Department of Science and Technology (DST) said this discovery shows exactly how BSSs are born.
Researchers zoomed in on binary star system TIC 327546480,about 9,500 light-years away in old star cluster Collinder 261. They picked it to see the interaction between two stars. Using NASA’s TESS light curves and radial velocity from Chile's Very Large Telescope,they got key data .
Annapurni Subramaniam from IIA,who co-authored the study,said the team saw the BSS taking material from its companion. This is rare glimpse of BSS forming. “Our finding offers direct observational evidence for one of the leading theories proposed to explain the origin of the BSS,” Subramaniam noted .
The system is semidetached,meaning one star's expanded enough to spill over its gravitational boundary,the Roche lobe . This overflow makes the smaller star give mass to the BSS . DST noted this mass transfer shows the rejuvenation process is active,making it one of clearest forming blue stragglers yet.
Besides mass transfer,they spotted strong X-ray emissions from the system . Analysis showed BSS is about 1.67 times Sun's mass,while its companion is around 0.32 solar masses. They orbit every 2.11 days with a low mass ratio of about 0.19. BSS spins fast at 69.55 km/s,likely sped up by its companion's material.
Modeling indicates mass transfer started about 5.46 billion years ago and still goes on. Cluster's age is around 7 billion years,giving context to BSS's timeline. Ali Hasan Sheikh,a PhD student at Gauhati University and lead author,was excited about what this means for understanding stars…
